1. Field of Invention
A rotary atomizer and a method of operating it.
The invention relates to a rotary atomizer of the kind in which a disc- or wheel-shaped atomizing device is secured to one end of a shaft which is connected with the rotor of a high frequency asynchronous electric motor. The operating speed of the motor is controlled by a frequency converter to impart to the shaft a rotational speed substantially higher than the first critical speed of the shaft and atomizing device.
2. Prior Art
In general, rotary atomizers in which the atomizing disc or wheel is directly driven by a high speed electric motor is known, e.g. from Keith Masters: "Spray Drying Handbook", 5th Edition, New York 1991, page 218. These offer the advantage that a gear transmission between the drive motor and the atomizer is not required. In some prior art atomizers of this kind a comparatively short rigid shaft carrying the atomizing device at its lower end has been coupled with the rotor of the high frequency motor.
With such a design, the necessity to operate the atomizer within a speed range safely below the first critical speed of the shaft and the atomizer wheel sets limits to the diameter range of atomizer wheels, for which a direct high frequency motor drive can be successfully used when the circumferential velocity required for atomization is to be achieved.
From U.S. Pat. No. 4,713,146 it is known to operate rotary atomizers at rotational speeds higher than the first critical speed of the rotating parts by a rather complicated shaft design involving incorporation of spring means between inner and outer shaft members to permit flexible pivotal motions of the shaft during start and stop of the atomizer.